Ballast circuitry for a great many fluorescent lamp systems is of the auto-transformer type which is undesirably heavy, cumbersome, and expensive as compared with most electronic-type circuitry. Moreover, autotransformer type ballast circuitry tends to be relatively inefficient of energy causing undesired heating which is obviously detrimental. Also, such apparatus operates in the audible frequency range which results in undue and undesired noise and is annoying to a user.
As to electronic type ballast circuitry, one form of such circuitry is set forth in U.S. Pat. No. 4,109,307. Therein, a charge storage and charge storage isolating capability is provided in apparatus which includes a high frequency inverter circuit. However, the high frequency inverter circuit is independent of unexpected load changes which is a less than satisfactory operational condition.
In another known form of electronic ballast circuitry, the high frequency inverter circuit is load dependent which enhances the operational capability. However, the drive system for the high frequency inverter circuit is relatively complex which, in turn, undesirably increases the component and assembly costs. Moreover, circuit complexity is usually in diametric opposition to enhanced reliability.
In still another form of electronic ballast circuitry, a load dependent high frequency inverter is utilized in conjunction with a charge storage and charge storage isolating circuit. Moreover, the high frequency inverter drive circuitry is relatively uncomplicated and a starting circuit initiates operation of the high frequency inverter. However, the starting circuit requires an amplifier system which adds complexity and expense to the apparatus.